Re: SMMU 2-stage support

[Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>]

On Fri, Apr 03, 2015 at 10:55:02AM +0100, Baptiste Reynal wrote:
> We are eventually working on the vSMMU implementation. Relying on the talk
> Will Deacon gave at the Linux Plumbers IOMMU Microconference on October
> 2014 (http://linuxplumbersconf.org/2014/ocw/proposals/2019), I tried the
> vSMMU initialization.

My position on the vSMMU still hasn't changed:

> > Anyway, until somebody actually wants this feature I've put it on ice as
> > it adds a whole bunch of complication to the ARM SMMU driver, as well as
> > new user ABI extensions that I don't really want to maintain for fun.

So, whilst it's great that you're looking at the code, I'm not very keen
on merging anything until we have people committed to using it. Right now,
the only feedback I've had has been going in the para-virt direction and I
don't think we should do this "for fun".

> I have a question about the KVM_DEV_ARM_SMMU_V2_CFG_INIT call. What is
> exactly expected as parameters ?

Yes, it's the IPA of the vSMMU device. I hacked something into kvmtool
when I was playing with this before:

  https://git.kernel.org/cgit/linux/kernel/git/will/kvmtool.git/commit/?h=kvmtool/vfio

Will